The present invention relates generally to a method for joining rigid substrates at abutting lateral edges to form a unitary substrate. Though not restricted to any particular use, the method is illustrated herein in the context of manufacturing a writing head for use in an electrographic marking device; the writing head has a head member comprised of multiple joined sections that are joined according to this method.
In an electrographic marking device, an exemplary writing head comprises a plurality of writing electrodes physically positioned to electrically address a dielectric surface of the medium as the medium travels through the writing station. An aligned series of backup electrodes is positioned opposite to the writing electrodes of the writing head in a manner that leaves a small gap, and the medium on which the image is to be formed passes through this gap. When the potential difference between the addressed writing electrodes and the opposed backup electrodes is raised to a threshold level of several hundreds of volts, referred to as the Paschen breakdown point, an electrostatic charge is deposited on the dielectric portion of the medium as that medium is moved through the gap. The timing and sequencing of energization of the electrodes provides for electrical charging of selected areas of the medium to form a desired latent image as the medium is moved through the writing station.
When the image to be formed on the medium is considered to be structured as a two-dimensional array of rows and columns of image spots, the latent image is typically formed row by row (or column by column), requiring the writing head to contain a writing electrode, referred to as a "nib" herein, for each spot to be formed in a row (or column) of the image. Thus, the writing head must be as wide as the visible image desired, which is typically related to the width of the medium, and the nibs must be as closely spaced as necessary to form a visible image having the desired resolution while still being able to be independently controlled. The closely spaced nibs form a line referred to as the "nib line" of the writing head; each row of the latent image produced by the nib line is referred to as a "scan line" of the image.
U.S. Pat. Nos. 3,693,185 and 3,793,107, issued to Lloyd, (hereafter also referred to as the Lloyd patents) disclose a method of construction of an electrostatic writing head that involves winding a length of wire about a mandrel to form uniformly laterally spaced convolutions of wire. An elongated strip of insulating material that is coated with a hardenable adhesive material extends transversely to the plane of the uniformly spaced wire convolutions and is positioned beneath them. This coated strip, which ultimately forms a first head member of the writing head, is then moved radially outwardly of the convolutions to urge the adhesive material against portions of the convolutions. Then another strip of insulating material is adhered to the convolutions in confronting relation to the first named strip so as to sandwich portions of the convolutions between the confronting strips. The strips are then compressed tightly together and after permitting the adhesive material to harden, the convolutions and strips are severed by cutting through both the strips and the convolutions along a line extending lengthwise of the strips; each of the two lines of wire tips exposed by the cutting operation forms the nib line of a writing head.
Writing heads may be made in a variety of widths using this process, which provides flexibility for producing multiple smaller-width writing heads from a single winding. For wide image marking requirements, however, such as for devices that support engineering, architecture and graphic arts applications, the writing heads are typically made in single, full-width units. The maximum width of a nib line is subject to the capabilities of the winding apparatus, and considerable retooling of equipment would be required to enlarge the width.
Thus, it is apparent that there is a manufacturing limitation with respect to producing writing heads of varying widths according to the process disclosed in U.S. Pat. Nos. 3,693,185 and 3,793,107 and having the structural configuration shown therein.